Lori Moore, 33, was annoyed – but not afraid. After all, Jason had never been menacing before, even though their divorce had been unpleasant. "She said he might turn up at the reunion," her friend Keely Absher tells PEOPLE. "And we sort of rolled our eyes and were like, 'Oh, the drama.' But no one had any idea that he was planning to do anything more."

But when Jason, 40, showed up at the Fifth Quarter Sports Bar and Pizzeria in East Peoria on June 14, he clearly had a plan.

After chatting with some acquaintances, Jason approached Lori and her new boyfriend, Lance Griffel. Calmly and wordlessly, he shot them each in the head, eyewitnesses tell PEOPLE, killing them both. He then turned the gun on himself but missed because he flinched as he pulled the trigger. A concerned bystander tackled him as an off-duty FBI agent shot Jason, killing him almost instantly.

Contentious Texts

The senseless and sudden act of violence has stunned the East Peoria community. Although Jason and Lori had exchanged several contentious text messages in the five hours before the shooting, it didn't seem like there was anything to worry about. "I've seen domestic cases with a lot more intense language," says East Peoria Police Chief Dick Ganschow in a press conference, "and they didn't end this way."

The texts, obtained by PEOPLE, started out civilly. Jason told Lori that he was "cool" with her new relationship with Griffel, 35, but worried about their financial agreements. "If you guys get real serious and live together, please reconsider our child support agreement," he wrote. "I'm struggling to make ends meet." According to their divorce agreement, he was paying $1,000 a month in child support. Police add that Jason had recently refilled prescriptions for an antidepressant and a sleep aid.

The conversation took an unpleasant turn when Jason offered to watch the couple's two kids, son Kaydin, 9, and daughter Callie, 4. "You can leave them with me, so you guys can go," he wrote. Lori thanked him for his offer, but declined. "I wasn't trying to be nice to you," he retorted. "I just wanted my kids."

When she didn't reply, he wrote, "Ok. I'll see you at 5th quarter." She replied, "Creepy."

The communication escalated from there, with Jason firing off seven angry text messages within five minutes, complaining about his child-support payments and her new relationship. Despite their subject matter, the texts did not contain threats or profanity. According to police, Jason finished texting and headed toward the sports bar where the reunion was being held.

A Devoted Mother

But behind the salacious headlines and combative text messages was a woman whom friends knew as a devoted mother. In casual conversation, Lori affectionately referred to son Kaydin as "The Boy" and boasted about his intelligence and quick wit. She joked about the unbridled energy of her smiley daughter, Callie.

"Lori would tell everyone that her kids were her entire life," says her friend Absher. "She was very focused on being a good mother to them. You didn't have to spend much time with her to know that they had a strong bond. She loved them more than anything, and they loved her back."

Several months after Lori and Jason divorced, she put up a profile on Match.com, where she caught the eye of Griffel, an engineer who worked at the same company that she did. Sparks flew, and they began dating. Neither of them had any idea about what would happen. "Lance was just a guy dating a girl," says Absher. "He certainly didn't deserve this."

Friends and family are concerned about the future of Kaydin and Callie, who are left without either parent. (The family has set up a GoFundMe page for their future.)

"Obviously, it can't make up for them losing their mom," says Absher, "but maybe we can come together and provide some sense of comfort during this unimaginably hard time."